Stripping Vallejo  polyurethane primer is not like stripping any other paint.  Your best bet is to use the purest isopropyl alcohol you can get and give it a long soak and multiple scrubs.  I've tired various other strippers such as Simple Green, Windex, and SuperClean and they barely touched it.  I have not tried oven cleaner nor brake fluid, but I don't know why you would even want to mess with them.

You can also use denatured alcohol, but it is a mix of various alcohols and other solvents, one of which is acetone.  Soaking plastic in denatured alcohol can melt the plastic, but will more likely result in softening it which won't be apparent until you try to scrub the paint off.